How to model a ribbon
Start with a bezier circle.  In edit mode, scale along Y-axis so that it is squashed.  Add an extrude factor to form the main part of the bow.  Add another circle for the centre part of the bow and a bezier curve for the bottom strands.  



Convert all three objects to a mesh with ALT+C.  In Edit mode, add some loops lengthwise to all three objects to support the deformations.

For the main bow, add a simple deform set to Twist to give it a more realistic look.  Create a new Lattice at the origin and add a lattice modifier to the bow.  Modify the lattice in edit mode to create the distinctive bow shape.

Add a subdivision surface, solidify and bevel modifier to the object to give it some thickness.

Repeat the process for the other parts of the bow.  You may need to tweak the modifiers to avoid any intersecting faces.